Preparation of chemically pure tungsten and molybdenum trioxide



Patented July 21, 1931 PATENT FFKfE PAUL SCHWARZKGPF, F BERLIN, GE-R1YLANY, ASSIGNQR 'i-O AMERICAN ELECTRO METAL CORPORATION, OF NEW YORK, LT. Y.

lREPAB-ATEON 0F CHEIKICALLY PURE TUNGSTEN AND LMOLY'BDENUM TRIOXIDEE No Drawing. Application filed July 1 3;, 1928, Serial 11o. 2 2,913, and in Sci-many July 20, 1-927.

The present invention relates to a process for preparing chemically pure tungsten and molybdenum trioxide in an inexpensive manner and at temperatures at which, with .ordinary methods, only a very small portion of tungsten or molybdenum would be able to evaporate. For carrying out the process, a carbon from a cheap source, as coke for in.- stance, is used which has the advantage that not only. a receptacle of a cheap grade of material can be used, on account of diminished strain at the lower temperature, but also that the yield is considerably increased as 96% or more of chemically pure trioXide is obtained.

In the known methodsof producing tungsten and molybdenum trioxide, in which these oxides are obtained from solid or molten mixtures or compounds by sublimation or evaporation and subsequent condensation, and also the methods in which the same way is adopted, involving the gaseous phase and starting from initial materials containing metallic tungsten or molybdenum, these initial mate rials being exposed at high temperatures to the action of oxygen, the inventor has found that the complete conversion of the tungsten or molybdenum present in the initial material, into gaseous trioxide involves difficulties in all cases in which an accumulation of iron oxide. manganese oxide and similar oxides as well as silica and silicates is possible in the sublimation or distillation residue.

These compounds hinder chemically or mechanically the volatilization of trioxides present or formed, so that iii-proportion as their percentage increases in the residue, higher temperatures must be used, in order to carry out the production of gaseous trioxides at a velocity which is of practical utility.

The following experiments show that the said oxides and silicates are actually the cause of the retardation of the velocity of evaporation at a given temperature:

1.- Ch m y p re M 3, in a molt n state, an be on t d mp et ly into vapour form at 800 Q. at a considerable velocity, if care is taken at he vapour ormed is rapidly conveyed away by passing air .orer the surface of the liquid.

If however 10% .of its weight of iron oxide is introduced into the evaporating melt, the evaporation ceases immediately and cannot be carried out completely even at 1-200 2. If chemically pure tungsten metal in e form of powder is burned in a stream 0f onygen or a mixture of oxygen and air, a complete conversion of the metal into G vapour is possible at about 1200 C. in the case of tungsten powder, which contains only 0.2% SiO and 2% Fe O there rem Xe hind at this temperature with otherwise similar conditions, a residue which gives oil no more V0 vapours, although it still conta 1- 40% of the tungsten originally present. Even at a temperature which is higher 1 to 400 C., the extraction of tungsten as from this residue by evaporation and subsequsl t Condensation is only possible to a small deg e A a mo t all the raw m e al f r he methods eferred to a o e t n ron in metallic or oxidic form and silica, and since in view of the material of the crucibles or other receptacles, in which these processes are carried .out, the temperatures employed can only be increased Within small limits, it was necessary hitherto in these processes to be satisfied with relatively poor yields, i. e. to leave some of the tungsten or molybdenum behind in the residues, which could no longer be Worked up by the methods invelving the gaseous phase.

The method according to the invention avoids residues, that is to'say supplies a practically hundred percent yield and has also the advantage of being substantially less expensive than the'distillation and sublimation processes employed hitherto and which are in themselves incomparably cheaper than the chemical processes.

According to the invention, porous, carboncontaining material, more especially coke other similarly distilled porous types ct coal can also be used) is mixed with the raw materials containing tungsten or molybdenum to be Worked up, and the resulting mixtures are exposed to the action of mixtures of oxygen it: I

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and air, after the coke has been ignited at some point.

The inventor has observed that the admixture of colre has a two-fold eli'ect:

In the first place it supplies by partial combustion the heat required for carrying out the processeither alone or when working up raw materials containing tungsten or molybdenum in metallic form, together with these metals whicn supply substantial quantities of heat during their oxidation, so that if correctly proportioned it is not necessary to heat the crucible or other receptacle from outside, and secondly the coke absorbs the metal oxides and silicates which have become liquid and accumulate in the residue at the temperature (about 300 C.) at which the process is carried out owing to the evaporation of the tungsten or molybdenum, which causes the coke to form a slag with these oxides and silicates thus enabling a complete conversion of the tungsten or molybdenum into gaseous trioxide at temperatures at Which only the first portion of the tungsten or molybdenum would have been able to be evaporated without the addition of coke.

The quantities of carbon to be added must naturally be varied according to the composition of the initial materials, but even in the case of initial materials with 50% foreign substances, an addition of 10 to 15% f the weight of the raw material is sullicient for obtaining yields of 96% and more of chemically pure trioxide.

The obtaining of higher yields and the possibility of working up such materials, which could not be worked up according to the sublimation and distillation processes hitherto known, is however, as mentioned, only one of the advantages of the new process. The second lies in the possible omission of any external heating.

Not only can the apparatus required for carrying out the process be simpler and the carbon which burns be in most cases a cheaper source of energy than illuminating gas or electricity, but also it will be immediately rec ognized that an important advantage lies in the diminished strain on the material of the receptacle and in the possibility of using cheaper materials for the receptacles.

In the new method the crucible merely plays the part of a reaction vessel, which, protected against external influences by embedding, can be kept colder than the reaction mass itself, whereas in the former methods it also served as heating vessel and was thus exposed on its surface to the destructive action of the flaming gases or electrolytic processes and to unavoidable differences in temperature; in addition owing to heat being carried away by the cvaporating trioxides and the streams of air or oxygen which were employed in most cases, it had to be heated to higher temperatures than would be required for carrying out the process.

Moreover the new method can be carried out in the same apparatus as that described by the inventors of the new method in U. S. Patent No. 1,629,004: (Serial Number 124350) except that the heating coil used there for heating the crucible together with all the devices for supplying the current can be omitted.

The regulation of the temperature is effected here by varying the velocity of the stream of gas moving over the surface of the contents of the crucible and varying its composition, by mixing more or less oxygen with the stream of air. By this means in the same way as in the older process of the same inventor, it is possible in this process also to separate the tungsten from the molybdenum in the case of initial materials containing both these heavy metals, in the same way as the separation takes place from all other constituents, vapourising more readily and with more dilficulty, in the initial material.

The quality of the trioxides produced after condensation does not difier in any way from tiat of the products which are obtained according to the older process.

Naturally it is also possible to combine the older process with the new by first proceeding according to the old process and working up the remaining residues according to the new process.

The initial materials of the process may be ores, preferably after roasting, and metal waste (or mixtures of the same).

The carbon-containing materials added are preferably used in granular or powder form.

hat I claim is 1. A process for the production of a chemically pure substance of the group consisting of tungsten trioxide and molybdenum trioxide consisting in adding porous, carboncontaining material to the primary material containing one of the substances tungsten and molybdenum, subjecting the resulting mass to heat treatment in the presence of a current containing-oxygen, and obtaining the trioxide therefrom.

2. A process for the production of a chemically pure substance of the group consisting of tungsten trioxide and molybdenum trioxide consisting in adding porous, carboncontaining material to the primary material containing one of the substances tungsten and molybdenum, subjectng the resulting mass to heat treatment in a current of mixtures of oxygen and air, and obtaining the trioxide therefrom.

3. A process for the production of a chemically pure substance of the group consisting of tungsten trioxide and molybdenum trioxide consisting in adding porous, carboncontaining material to the primary material containing one of the substances tungsten and molybdenum, igniting the said carboncontaining material, subjecting the mass to the action of a current of oxygen and obtaining the trioxide therefrom.

at. A process for the production of a chemically pure substance of the group consisting of tungsten trioxide and molybdenum trioxide consisting in adding porous, carboncontaining material to the primary material containing one of the substances tungsten or molybdenum, igniting the said carboncontaining material, subjecting the mass to the action of a current of mixtures of oxygen and air and obtaining the trioxide therefrom.

5. A process for the production of a chemically pure substance of the group consisting of tungsten trioxi-de and molybdenum trioxide consisting in adding coke to the primary material containing one of the substances tungsten and molybdenum, subjecting the resulting mass to heat treatment in the presence of a current of oxygen and obtaining the trioxide therefrom.

6. A process for the production of a chemically pure substance of the group consisting of tungsten trioxide or molybdenum trioxide, consisting in adding coke to the primary material containing one of the substances tungsten and molybdenum, subjecting the resulting mass to heat treatment in the presence of a current of mixtures of oxygen and air, and obtaining the trioxide therefrom.

7. A process for the production of a chemically pure substance of the group consisting of tungsten and molybdenum trioxide, consisting in first obtaining one of said trioxides from the unmixed primary material containing one of the substances tungsten and molybdenum, thereupon treating the residues only with carbon-containing material, oxidizing the same and obtaining the trioxide therefrom.

8. A process for the production of a chemically pure substance of the group consisting of tungsten trioxide and molybdenum trioxide, said process consisting in first obtaining one of said trioxi-des from an unmixed primary material containing one of the substances tungsten ancl molybdenum, thereupon treating the resulting mass with carbon-containing material, oxidizing the same and obtaining the trioxide therefrom.

In testimony whereof I have signed my name to this specification.

PAUL SCHl/VARZKOPF. 

